When it comes to Dommes, sessions and how they approach that work (and fun) the only truth is that everyone is different. So, the things I am going to mention may apply to just a few or may apply to a majority of Dommes but definitely some and definitely not all... So, whether it matters is really just personal preference on the Domme's part.

For some, the play within a session is also a performance so blindfolding the sub means they don't have to pay attention to the visual part of what the sub is experiencing for at least part of it (and they can dip in and out of it by sliding the blindfold off for a few seconds at a time and putting it back on). That takes a bit of pressure off of them.

Another reason for some is that they don't have to wear heels or corsets the whole time (I have been told by several Dommes that as soon as the blindfold goes on, the heels come off). I have noticed, more than once, a different "costume" at the end of the session than what a Domme was wearing when I first entered the room (and since I don't make clothing requests, I have told Dommes that if something is uncomfortable then not to put it on in the first place for me... But, the reply is usually that putting those things on is part of what gets then into that headspace so it is more about them than me).